Hi Guys, This is only my second project using arduino, so any help and advice you can give me would be really welcome. Basically I want to control the speed fairly precisely of a Universal motor from a washing machine running on 240V AC. In the past I have made and used a simple triac controller to do this, but the speed regulation is quite poor under heavy load (I am using it to drive a lathe spindle). What I want to do is take the signal coming from the tachometer that is on the end of the motor (washing machine motors seem to typically come bundled with these) and make sense of it with the arduino. Doing this on its own, would be quite cool as a spindle speed calculation and display should then be quite easy. Question is, how do I have to treat the signal from the tacho before feeding it in? From measuring it with the multimeter I can see it goes up to about 20V with the motor spinning fast (although the current always stays very low), so presumably I would need a voltage regulator of some kind? Or would a simple resistor do?
I am guessing that it may be best to use the pulse to trigger the gate of a transistor and use that to give nice clean 5V pulses that the arduino can count? But what kind of transistor to use?
From what I have read the taco is likely to provide 8 pulses per revolution of the motor shaft. Considering the motor can spin over about 20k RPM (it has a large reduction gear on it so the lathe spindle speed is a fraction of that) that’s a lot of pulses...
I have had some success in using the arduino to control the triac circuit, by replacing the POT with a photo resistor which is paired with an LED I vary from the arduino. So once I can reliably read form the tacometer I can then start thinking about using the information to provide feedback for speed regulation. Any help most welcome!